diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 34a802c6..66d1add4 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -5,6 +5,11 @@ on:
     branches: [main, develop, 'feature/**', 'hotfix/**', 'release/**']
   pull_request:
     branches: [main, develop]
+  # Nightly, on the default branch: the browser tests in Firefox and WebKit as well as
+  # Chromium, which pull requests run alone to stay fast.
+  schedule:
+    - cron: '30 3 * * *'
+  workflow_dispatch:
 
 jobs:
   tests:
@@ -238,6 +243,11 @@ jobs:
     # authoritative: a deployment dumped with --classmap-authoritative answers
     # from the classmap alone. Theme and plugin classes are autoloaded at
     # runtime, and every front-end page once answered 404 there (#320).
+    # Chromium on pushes and pull requests; all three engines on the nightly and on a
+    # manual run.
+    env:
+      E2E_BROWSERS: ${{ (github.event_name == 'schedule' || github.event_name == 'workflow_dispatch') && 'chromium,firefox,webkit' || 'chromium' }}
+
     strategy:
       fail-fast: false
       matrix:
@@ -328,7 +338,7 @@ jobs:
         working-directory: packages/framework/tests/e2e
         run: |
           npm ci
-          npx playwright install --with-deps chromium
+          npx playwright install --with-deps ${E2E_BROWSERS//,/ }
 
       # DDEV serves HTTPS with a mkcert certificate when mkcert is present.
       # Say which case the runner is in rather than guessing.
diff --git a/tests/e2e/fixtures/plugins/e2e-features/app/Endpoints/Translations.php b/tests/e2e/fixtures/plugins/e2e-features/app/Endpoints/Translations.php
new file mode 100644
index 00000000..67ff1f04
--- /dev/null
+++ b/tests/e2e/fixtures/plugins/e2e-features/app/Endpoints/Translations.php
@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Plugin\E2eFeatures\Endpoints;
+
+use Pollora\Attributes\WpRestRoute;
+use Pollora\Attributes\WpRestRoute\Method;
+
+/**
+ * What `__()` answers, on each side of the helper that shares the name: WordPress keeps
+ * its own as `__wp()`, and `__()` sends a call with a text domain to WordPress and a call
+ * with replacements to Laravel. This plugin's fr_FR catalogue is what WordPress finds,
+ * whatever the site's language.
+ */
+#[WpRestRoute('e2e/v1', '/translations')]
+class Translations
+{
+    /** @return array{wordpress: string, untranslated: string, laravel: string, wpNative: string} */
+    #[Method('GET')]
+    public function show(): array
+    {
+        // Loaded as the catalogue of the current locale, whatever the site's language:
+        // since WordPress 6.5 translations are kept per locale, so loading it as fr_FR
+        // on an en_US site would leave __() nothing to find.
+        unload_textdomain('e2e-features');
+        load_textdomain('e2e-features', WP_PLUGIN_DIR.'/e2e-features/languages/e2e-features-fr_FR.mo', determine_locale());
+
+        return [
+            'wordpress' => __('E2E greeting', 'e2e-features'),
+            'untranslated' => __('E2E string outside the catalogue', 'e2e-features'),
+            'laravel' => __('Shipping :brand', ['brand' => 'Example']),
+            'wpNative' => __wp('E2E greeting', 'e2e-features'),
+        ];
+    }
+}
diff --git a/tests/e2e/fixtures/plugins/e2e-features/languages/e2e-features-fr_FR.mo b/tests/e2e/fixtures/plugins/e2e-features/languages/e2e-features-fr_FR.mo
new file mode 100644
index 00000000..60a64038
Binary files /dev/null and b/tests/e2e/fixtures/plugins/e2e-features/languages/e2e-features-fr_FR.mo differ
diff --git a/tests/e2e/fixtures/plugins/e2e-features/languages/e2e-features-fr_FR.po b/tests/e2e/fixtures/plugins/e2e-features/languages/e2e-features-fr_FR.po
new file mode 100644
index 00000000..15ce14ff
--- /dev/null
+++ b/tests/e2e/fixtures/plugins/e2e-features/languages/e2e-features-fr_FR.po
@@ -0,0 +1,13 @@
+# Pollora browser test fixture: the catalogue the i18n test reads in fr_FR.
+msgid ""
+msgstr ""
+"Project-Id-Version: E2E Features\n"
+"Language: fr_FR\n"
+"MIME-Version: 1.0\n"
+"Content-Type: text/plain; charset=UTF-8\n"
+"Content-Transfer-Encoding: 8bit\n"
+"Plural-Forms: nplurals=2; plural=(n > 1);\n"
+"X-Domain: e2e-features\n"
+
+msgid "E2E greeting"
+msgstr "Bonjour depuis le catalogue"
diff --git a/tests/e2e/playwright.config.ts b/tests/e2e/playwright.config.ts
index 9ee9ee1f..f0b3451e 100644
--- a/tests/e2e/playwright.config.ts
+++ b/tests/e2e/playwright.config.ts
@@ -9,6 +9,7 @@ import { defineConfig, devices } from '@playwright/test';
  * WP_BASE_URL    WordPress itself (`siteurl`), e.g. https://pollora-test.ddev.site/cms/ —
  *                read by @wordpress/e2e-test-utils-playwright for wp-admin, login and REST
  * E2E_WP_CLI     how to run WP-CLI against that site, e.g. "ddev wp" (default)
+ * E2E_BROWSERS   comma-separated: chromium (default), firefox, webkit — the nightly runs all three
  */
 const homeUrl = process.env.E2E_HOME_URL ?? 'https://pollora-test.ddev.site';
 // Trailing slash: relative paths such as wp-login.php must resolve inside /cms.
@@ -29,6 +30,20 @@ if (! process.env.NODE_EXTRA_CA_CERTS) {
     }
 }
 
+const browsers: Record<string, string> = {
+    chromium: 'Desktop Chrome',
+    firefox: 'Desktop Firefox',
+    webkit: 'Desktop Safari',
+};
+
+const projects = (process.env.E2E_BROWSERS ?? 'chromium').split(',').map((name) => name.trim()).map((name) => {
+    if (! (name in browsers)) {
+        throw new Error(`E2E_BROWSERS: unknown browser "${name}" (known: ${Object.keys(browsers).join(', ')})`);
+    }
+
+    return { name, use: { ...devices[browsers[name]] } };
+});
+
 export default defineConfig({
     testDir: './specs',
     globalSetup: './global-setup.ts',
@@ -46,5 +61,5 @@ export default defineConfig({
         screenshot: 'only-on-failure',
         video: 'retain-on-failure',
     },
-    projects: [{ name: 'chromium', use: { ...devices['Desktop Chrome'] } }],
+    projects,
 });
diff --git a/tests/e2e/specs/features.spec.ts b/tests/e2e/specs/features.spec.ts
index d16eed5c..da4cd76c 100644
--- a/tests/e2e/specs/features.spec.ts
+++ b/tests/e2e/specs/features.spec.ts
@@ -163,6 +163,21 @@ test.describe('Assets', () => {
     });
 });
 
+test.describe('Translations through __()', () => {
+    test("a text domain goes to WordPress's catalogues, replacements to Laravel", async () => {
+        const context = await visitor();
+        const translations = await (await context.get(homeUrl('/wp-json/e2e/v1/translations'))).json();
+        await context.dispose();
+
+        expect(translations).toEqual({
+            wordpress: 'Bonjour depuis le catalogue',
+            untranslated: 'E2E string outside the catalogue',
+            laravel: 'Shipping Example',
+            wpNative: 'Bonjour depuis le catalogue',
+        });
+    });
+});
+
 test.describe('The active theme', () => {
     test('registers the menu locations its config/menus.php declares', async ({ requestUtils }) => {
         const configFile = join(siteDir, 'themes', activeTheme(), 'config', 'menus.php');